1. Field of the Invention
The present invention relates to a photoacoustic measurement apparatus that measures biological information on the basis of the photoacoustic effect.
2. Description of the Related Art
Ongoing research and development is being conducted on technologies for non-invasive visualization of biological information using high-transmittance near-infrared light. Biological constituent elements, such as water, fats, hemoglobin in blood vessels and so forth have characteristic spectra in the near-infrared wavelength band. Therefore, attention is being given to research aimed at obtaining functional information in-vivo through visualization of the spatial distribution of absorption coefficients from the above constituent elements.
The photoacoustic effect is a phenomenon whereby an object generates acoustic waves (typically, ultrasonic waves) when irradiated with pulsed light. These acoustic waves arise from volume expansion at regions that have a high absorption coefficient, within the subject to be measured. A photoacoustic measurement apparatus detects and reconstructs the generated acoustic waves by way of an acoustic wave detector. The spatial distribution of the absorption coefficients can be displayed as a result. Compared to light, acoustic waves have higher penetration into a biological body, and hence photoacoustic measurement apparatuses that rely on acoustic wave detection boast high spatial resolving power. In the present invention, the term “photoacoustic wave” denotes acoustic waves generated on account of volume expansion as a result of pulsed light irradiation.
Imaging equipment that exploits the photoacoustic effect includes, for instance, the device set forth in US Patent Application Publication No. 2006/0184042, which discloses a photoacoustic microscope that detects photoacoustic waves with high resolving power, by arranging a light source and an acoustic wave detector on a same side of a biological body. Light is irradiated in oblique incidence, from a side of the acoustic wave detector, in order to concentrate light in a region within the biological body.